buildroot

docs: update URL to uClibc-ng homepage

It is not necessary to update all mentioning of uClibc, but
at least we should point to the right homepage of the used
project.

Signed-off-by: Waldemar Brodkorb <wbx@openadk.org>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>